1. Field of the Invention
The invention relates to a display device displaying pictures by driving light emitting elements by current, which are arranged at each pixel. Particularly, the invention relates to a so-called active matrix display device which controls a current amount flowing in the light emitting element such as an organic EL by an insulated-gate field effect transistor provided in each pixel circuit. In addition, the invention relates to electronic equipment in which such display device is incorporated.
2. Description of the Related Art
In a display device, for example, in a liquid crystal display, a lot of liquid crystal pixels are arranged in a matrix state, and pictures are displayed by controlling transmittance intensity or reflectance intensity of incident light by each pixel according to picture information to be displayed. The same applies to an organic EL display using organic EL elements in pixels, however, the organic EL element is a self-light emitting element, which is different from the liquid crystal pixel. Therefore, the organic EL display has advantages such that visibility of pictures is high as compared with the liquid crystal display, that a backlight is not necessary and that response speed is high. In addition, luminance level (gradation) of each light emitting element can be controlled according to a current value flowing in the element, and the organic EL display is totally different from a voltage controlled type such as the liquid crystal display in a point that the EL display is a so-called current controlled type.
In the organic EL display, there are a simple matrix system and an active matrix system as a drive system thereof as is the case with the liquid crystal display. Though the former has simple configuration, it has problems such that it is large and it is difficult to realize high-definition display, therefore, the active matrix system are developed extensively at present. In the system, electric current flowing in the light emitting element in each pixel circuit is controlled by active elements (generally, thin-film transistors, TFTs) provided in the pixel circuit, which is disclosed in JP-A-2003-255856, JP-A-2003-271095, JP-A-2004-133240, JP-A-2004-029791 and JP-A-2004-093682.